Neither is more effective. The best way to get into Cambridge is to be good enough to get into Cambridge.
Now, depending on your subject there may be some colleges you don't want to apply for. Most significantly, applying for Maths at Trinity is one of the few subject and college combinations where you put yourself at a disadvantage when applying. Similarly with CS at Churchill or Trinity (STEM at Trinity, and to a lesser extent colleges like Churchill tends to be quite significantly oversubscribed, although this doesn't matter if you are planning on applying for humanities. At the very least I'm not aware of anything similar for humanities ).
However, aside from this you would be better put revising rather than trying to game the system. Hell if you try and "beat" the system by looking at admission statistics and the like you could very well screw yourself over as applications per college for a specific course can vary by significant amounts in consecutive years (even doubling in number), and even if you were to somehow gain an "advantage", it would be minuscule at best.
Also do look at things like location. You do have to travel to lectures, and being on the opposite side of Cambridge is not fun. Perhaps look into the Director of Studies for the college too, although I will admit this is very difficult to research about. Some DoS's are absolutely great people who will make your education significantly easier. Others, you hear... interesting stories about them.